1. Field of the Invention
The present invention relates to a holding plate to which a wafer is adhered through a wax, and a polishing method which is carried out by using the holding plate.
2. Description of the Related Art
A wafer is polished as follows. A wafer is adhered to a holding plate. The wafer is pressed against a polishing pad which is spread on a turn table, by the holding plate. The wafer is rubbed with the polishing pad. As a method in which the wafer is adhered to the holding plate, there are a wax-mounting polishing method and a waxless-mounting polishing method. As compared with the wax-mounting polishing method, the waxless-mounting polishing method has the advantages of good productivity and low cost because it is not necessary to carry out an adhesion operation in which the wafer is adhered to the holding plate and a separating operation in which the wafer is separated from the holding plate and the polished wafer is easily cleaned. However, in the waxless-mounting polishing method, there are problems about a flatness of the polished wafer, a local etching of a rear surface of the wafer, which is carried out by using an abrasive slurry, and the like. At present, the wax-mounting polishing method is used mainly.
In one wax-mounting polishing method, the wafer is chucked by a vacuum chucking apparatus to apply the wax to the rear surface of the wafer. The rear surface of the wafer is directed downwardly. The wafer chucked by the vacuum chucking apparatus is released near the holding plate to drop the wafer on the holding plate by a self-weight thereof. Thereby, the wafer is adhered to the holding plate. In another wax-mounting polishing method, the center portion of the rear surface of the wafer is pressed against the holding plate by a vacuum chucking apparatus into which an air pad is incorporated in a situation that the wafer to which the wax is applied remains chucked or in a situation that the wafer is curved. In this situation, the wafer chucked by the vacuum chucking apparatus is released. Thereby, the wafer is adhered to the holding plate. A holding plate which is made of glass, such as borosilicate glass or the like, or which is made of ceramics, such as alumina, silicon carbide or the like, is used. As the requirement for a flatness of a wafer becomes severe, a holding plate made of ceramics, which has a high rigidity is mainly used.
However, because the wafer has a warp, a flexure, an undulation or the like, bubbles are often sealed between the holding plate and the rear surface of the wafer after the adhesion. When there are bubbles between the holding plate and the rear surface of the wafer, part of the front surface of the wafer, which corresponds to the bubbles bulges out. When the wafer is polished, the part corresponding to the bubbles is polished more than the other parts of the front surface of the wafer. There is a problem that a dimple is caused in the wafer after the wafer is polished. Further, after the wafer is polished, a dimple is caused in the wafer partially by unevenly applying the wax to the wafer.
The present invention was developed in view of these problems.
An object of the present invention is to provide a holding plate having a construction in which bubbles are hard to be sealed between the holding plate and the rear surface of the wafer even by the wax-mounting polishing method and the thickness of the wax can be even, and to provide a polishing method in which the wafer can be polished by the holding plate so that the dimple is not caused after the wafer is polished.
That is, in accordance with an aspect of the present invention, the polishing method for wafer, comprises the steps of; adhering a wafer to a wafer adhesion part of a holding plate through a wax, and rubbing the wafer with a polishing pad, wherein grooves are formed on the wafer adhesion part and extend to the outside of the wafer adhesion part.
In such a polishing method, because the wafer is polished by using the holding plate in which the grooves are formed on the wafer adhesion part and extend to the outside of the wafer adhesion part, the air to be sealed between the wafer and the holding plate escapes to the outside of the wafer adhesion part through the grooves and is released into the atmosphere. Further, when the wax is unevenly applied to the wafer, the unnecessary wax flows into the grooves and the thickness of the wax becomes thin and even as a whole. As a result, after the wafer is adhered to the holding plate, it is prevented that the bubbles are sealed between the holding plate and the rear surface of the wafer and that the unnecessary wax gathers therebetween. The dimple can be prevented from being caused.
The grooves may be formed on the whole wafer adhesion part. The grooves may be formed at least on a portion of the wafer adhesion part, which is distant over a half of a radius of the wafer from a center of the wafer adhesion part.
In accordance with another aspect of the present invention, the polishing method for wafer, comprises the steps of; adhering a wafer to a wafer adhesion part of a holding plate through a wax, and rubbing the wafer with a polishing pad, wherein a surface roughness of at least a portion of the wafer adhesion part, which is distant over a half of a radius of the wafer from a center of the wafer adhesion part and that of a peripheral portion of the wafer adhesion part are approximately uniform, and an average roughness of the portion of the wafer adhesion part and that of the peripheral portion of the wafer adhesion part are from 0.5 to 1.5 xcexcm.
In such a polishing method, because the surface roughness is approximately uniform, and the average roughness is 0.5 to 1.5 xcexcm, the air to be sealed between the wafer and the holding plate easily escapes to the outside of the wafer adhesion part and is dispersed by many concaves between the wafer and the holding plate. As a result, after the wafer is adhered to the holding plate, it is prevented that the bubbles are sealed between the holding plate and the rear surface of the wafer. When the wax is unevenly applied to the wafer, the unnecessary wax flows into many concaves and the thickness of the wax becomes thin and even as a whole. As a result, an excellent polishing can be carried out without causing the dimple.
In accordance with another aspect of the present invention, a holding plate comprises; a wafer adhesion part for adhering a wafer through a wax, and grooves which are formed on the wafer adhesion part and extend to the outside of the wafer adhesion part.
In such a holding plate, because the grooves are formed on the wafer adhesion part and extend to the outside of the wafer adhesion part, when the wafer is adhered to the holding plate, the air to be sealed between the wafer and the holding plate easily escapes to the outside of the wafer adhesion part through the grooves. Further, when the wax is unevenly applied to the wafer, the unnecessary wax flows into the grooves and the unevenness of the thickness of the wax can be cleared. As a result, after the wafer is adhered to the holding plate, it is prevented that the bubbles are sealed between the holding plate and the rear surface of the wafer and that the unnecessary wax gathers therebetween. The thickness of the wax becomes even as a whole.
The grooves may be formed on the whole wafer adhesion part. The grooves may be formed at least on a portion of the wafer adhesion part, which is distant over a half of a radius of the wafer from a center of the wafer adhesion part.
The grooves may be formed in a grid shape, in a linear shape or in a concentrically circular shape, on the whole wafer adhesion surface of the holding plate.
The width of the grooves may be from 5 to 2000 xcexcm. The depth of the grooves may be from 2 to 500 xcexcm. The pitch of the grooves may be from 1 to 15 mm.
In accordance with another aspect of the present invention, a holding plate comprises; a wafer adhesion part for adhering a wafer through a wax, wherein a surface roughness of at least a portion of the wafer adhesion part, which is distant over a half of a radius of the wafer from a center of the wafer adhesion part and that of a peripheral portion of the wafer adhesion part are approximately uniform, and an average roughness of the portion of the wafer adhesion part and that of the peripheral portion of the wafer adhesion part are from 0.5 to 1.5 xcexcn.
In such a holding plate, because the surface roughness of at least the portion of the wafer adhesion part, which is distant over a half of a radius of the wafer from a center of the wafer adhesion part of the wafer adhesion surface and that of a peripheral portion of the wafer adhesion part are approximately uniform, and the average roughness thereof are 0.5 to 1.5 xcexcm, the air to be sealed between the wafer and the holding plate easily escapes to the outside of the wafer adhesion part and is dispersed by many concaves between the wafer and the holding plate. As a result, a polishing can be carried out without causing the dimple. When the wax is unevenly applied to the wafer, the unnecessary wax flows into many concaves and the thickness of the wax becomes thin and even as a whole.
According to the present invention, because the polishing method for wafer is carried out by adhering a wafer to a wafer adhesion part of a holding plate through a wax, and by rubbing the wafer with a polishing pad, wherein grooves are formed on the wafer adhesion part and extend to the outside of the wafer adhesion part, the air to be sealed between the wafer and the holding plate escapes to the outside of the wafer adhesion part through the grooves. Further, the unnecessary wax flows into the grooves. As a result, a polishing can be carried out without causing the dimple.